1. Field of the Invention
The present invention relates to a power transmission system that has a sealing structure, such as an end plate and a boot with an adapter, for sealing a constant velocity universal joint incorporated into an automotive propeller shaft or a drive shaft.
2. Description of the Related Art
As shown in FIG. 7, a power transmission system with a propeller shaft or a drive shaft for use in automobiles includes a so-called Lobro (or cross groove) constant velocity universal joint 5 having an inner ring 1, an outer ring 2, balls 3, and a cage 4 as its primary components. The power transmission system further includes a first shaft 6 (a stub shaft) coupled to the inner ring 1 of the constant velocity universal joint 5, and a boot 7 with an adapter attached to the first shaft 6 and the constant velocity universal joint 5 to seal the constant velocity universal joint 5. The power transmission system still further includes a second shaft 8 (a stub shaft) coupled to the outer ring 2 of the constant velocity universal joint 5 and provided at an end with a companion flange 10, and an end plate 9 disposed between the companion flange 10 of the second shaft 8 and the constant velocity universal joint 5 to seal the constant velocity universal joint 5.
The inner ring 1 of the constant velocity universal joint 5 has a splined bore 11 at its center and a plurality of track grooves 12 on its outer peripheral surface. The first shaft 6 is fitted into the splined bore 11 of the inner ring 1 to enable torque transmission, and then fixedly positioned axially in the inner ring 1 with a snap ring or a circlip 14 installed in an annular groove of the first shaft 6.
The outer ring 2 is disposed on the outer periphery of the inner ring 1 and provided on the inner peripheral surface of the outer ring 2 with the same number of track grooves 13 as that of the track grooves 12 of the inner ring 1.
The track grooves 12 of the inner ring 1 and the track grooves 13 of the outer ring 2 form angles opposite to each other with respect to the axial line. The track grooves 12 of the inner ring 1 are paired with the track grooves 13 of the outer ring 2 to form ball tracks 15, with the balls 3 being accommodated at the intersections between the track grooves 12, 13 for the ball tracks 15. The cage 4 is interposed between the inner ring 1 and the outer ring 2 to hold the balls 3 within pockets 16 of the cage 4. The boot 7 with an adapter for sealing the constant velocity universal joint 5 at an end is disposed between one axial end portion of the outer ring 2 and the first shaft 6 in order to prevent leakage of grease filled in the constant velocity universal joint 5 and intrusion of foreign material from outside. The boot 7 with an adapter includes a pleated rubber or plastic boot 7 having a reduced-diameter end portion and an enlarged-diameter end portion, and a metallic adapter 18 having a cylindrical portion 17 at an end. The enlarged-diameter end portion of the boot 7 and the other end of the adapter 18 are jointed together by caulking, and the reduced-diameter end portion of the boot 7 is fastened to the first shaft 6 with a boot band 19. Additionally, the cylindrical portion 17 of the adapter 18 is fitted onto an end portion of the outer ring 2 to be secured to the outer ring 2 with bolts 20.
The end plate 9 for sealing the constant velocity universal joint 5 at the other end is disposed between the other axial end portion of the outer ring 2 and the companion flange 10 in order to prevent leakage of grease filled in the constant velocity universal joint 5 and intrusion of foreign material from outside. The end plate 9 is formed in the shape of a bowl and provided at one end with a cylindrical portion 21, which is fitted onto the end portion of the outer ring 2 and sandwiched between the companion flange 10 and the end portion of the outer ring 2 to be secured with the bolts 20.
The aforementioned power transmission system is designed to prevent leakage of grease filled in the constant velocity universal joint 5 and intrusion of foreign material from outside. To this end, the boot 7 with an adapter for sealing the constant velocity universal joint 5 at an end is disposed between the one axial end portion of the outer ring 2 and the first shaft 6, and the end plate 9 for sealing the constant velocity universal joint 5 at the other end is disposed between the other axial end portion of the outer ring 2 and the companion flange 10.
To allow the adapter 18 and the end plate 9 to provide improved sealing performance, a gasket 22 is interposed between the adapter 18 and one end face of the outer ring 2 (see FIG. 7A), and a gasket 23 is interposed between the end plate 9 and the other end face of the outer ring 2 (see FIG. 7B). That is, annular recessed portions 24, 25 are provided on the inner peripheral edges at both axial end faces of the outer ring 2, and then the adapter 18 and the end plate 9 are secured to the outer ring 2 with the bolts 20, with the gaskets 22, 23 being fitted in the recessed portions 24, 25, respectively.
However, when the adapter 18 and the end plate 9 are attached to the outer ring 2, it is very difficult to position the gaskets 22, 23 at the recessed portions 24, 25 of the outer ring 2. Improper positioning of the gaskets 22, 23 would cause the gaskets 22, 23 to be dislocated, thereby impairing their sealing performance and making it difficult to prevent leakage of grease filled in the constant velocity universal joint 5 and intrusion of foreign material from outside.
In particular, in terms of the material of the gaskets 22, 23, rubber or cork gaskets are preferable to fluid or vulcanized rubber gaskets since they are inexpensive and impervious to impacts. However, there were problems with the aforementioned adapter 18 and the end plate 9 that they could be easily dislocated when incorporated into the outer ring 2.